Bi-prediction without signaling cu-level weights

ABSTRACT

Processing circuitry decodes information of a coding block in a current picture from a bitstream. The information indicates a bi-prediction mode without weight signaling. Weights associated with the bi-prediction mode are not signaled in the bitstream. Further, the processing circuitry determines a first motion vector associated with a first reference picture and a second motion vector associated with a second reference picture, and determine a first reference template in the first reference picture based on a current template of the coding block and the first motion vector and a second reference template in the second reference picture based on the current template and the second motion vector. The processing circuitry also calculates a weight for use in the bi-prediction mode based on the first reference template, the second reference template and the current template, and reconstructs the coding block using the bi-prediction with the calculated weight.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 63/179,928, “BI-PREDICTION WITH CU-LEVELWEIGHTS WITHOUT SIGNALING” filed on Apr. 26, 2021, which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Uncompressed digital video can include a series of pictures, eachpicture having a spatial dimension of, for example, 1920×1080 luminancesamples and associated chrominance samples. The series of pictures canhave a fixed or variable picture rate (informally also known as framerate), of, for example 60 pictures per second or 60 Hz. Uncompressedvideo has specific bitrate requirements. For example, 1080p60 4:2:0video at 8 bit per sample (1920×1080 luminance sample resolution at 60Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of suchvideo requires more than 600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding and/or decoding of spatially neighboring,and preceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode, submode, and/or parameter combination can havean impact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (110) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Motion compensation can be a lossycompression technique and can relate to techniques where a block ofsample data from a previously reconstructed picture or part thereof(reference picture), after being spatially shifted in a directionindicated by a motion vector (MV henceforth), is used for the predictionof a newly reconstructed picture or picture part. In some cases, thereference picture can be the same as the picture currently underreconstruction. MVs can have two dimensions X and Y, or threedimensions, the third being an indication of the reference picture inuse (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2, a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. For example, the processing circuitrydecodes information of a coding block in a current picture from abitstream. The information indicates a bi-prediction mode without weightsignaling. Weights associated with the bi-prediction mode are notsignaled in the bitstream. Further, the processing circuitry determinesa first motion vector associated with a first reference picture and asecond motion vector associated with a second reference picture for abi-prediction of the coding block, and determine a first referencetemplate in the first reference picture based on a current template ofthe coding block and the first motion vector and a second referencetemplate in the second reference picture based on the current templateof the coding block and the second motion vector. The processingcircuitry also calculates a weight for use in the bi-prediction modebased on the first reference template, the second reference template andthe current template, and reconstructs the coding block using thebi-prediction with the calculated weight.

According to some aspects of the disclosure, the current templateincludes one or more reconstructed samples that are neighboring to thecoding block. In some examples, the current template includes at leastone of one or more rows of samples above the coding block, and one ormore columns of samples to a left of the coding block. In some examples,the current template includes at least one of a row of samples that isimmediately above the coding block and a column of samples that isimmediately to a left of the coding block.

In some embodiments, the processing circuitry determines the weight thatminimizes a predefined cost function that is based on the firstreference template, the second reference template and the currenttemplate. In some examples, the predefined cost function is based onrespective samples differences of the current template to a predictedcurrent template that is predicted based on the first reference templateand the second reference template using a predefined bi-prediction modelwith one or more weight parameters.

In some examples, the predefined bi-prediction model includes threeweight parameters. The processing circuitry determines values of thethree weight parameters in the predefined bi-prediction model byordinary least squares.

In some examples, the predefined bi-prediction model includes two weightparameters. The processing circuitry determines values of two weightparameters in the predefined bi-prediction model by ordinary leastsquares.

In some examples, the predefined bi-prediction model includes one weightparameter. The processing circuitry determines a value of one weightparameter in the predefined bi-prediction model by ordinary leastsquares.

In some examples, the processing circuitry clips the weight(s) inpredetermined ranges.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIGS. 9A-9C show diagrams illustrating a uni-prediction of an intercoded coding block in some examples.

FIG. 10 shows a diagram of using bi-prediction for coding a videosequence according to some embodiments of the disclosure.

FIG. 11 shows a flow chart outlining a process of processing in abi-prediction mode according to an embodiment of the disclosure.

FIG. 12 shows a flow chart outlining a process according to someembodiments of the disclosure.

FIG. 13 shows a flow chart outlining an encoding process according to anembodiment of the disclosure.

FIG. 14 shows a flow chart outlining a decoding process according to anembodiment of the disclosure.

FIG. 15 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques for bi-prediction withoutsignaling CU level weights. Bi-prediction refers to techniques in interprediction that perform prediction for a block in a current pictureusing two references blocks that are respectively reside in tworeference pictures. In some examples, one of the two reference picturesis before the current picture in a video sequence, and the other of thetwo reference pictures is after the current picture in the videosequence, and the bi-prediction is referred to as bi-directionalprediction. According to some aspects of the disclosure, thebi-prediction techniques use prediction models with CU level weights.The CU level weights can be computed from previously decoded pixels, forexample, by fixed-point arithmetic, and the CU level weights are notsignaled in the bitstream.

In some related examples, bi-prediction with CU level weight (BCW) canuse fixed weights or weights that are signaled from the encoder side tothe decoder side at CU level (e.g., respectively for each CU).

In an example (e.g., HEVC), a bi-prediction signal (sample) is generatedby averaging two prediction signals (samples) obtained from twodifferent reference pictures and/or using two different motion vectors.For example, to predict a sample in a current picture using thebi-prediction, a first prediction signal is obtained by inter predictionbased on a first reference picture and a first motion vector, and asecond prediction signal is obtained by inter prediction based on asecond reference picture and a second motion vector. Then, thebi-prediction signal in the current picture is obtained by averaging thefirst prediction signal and the second prediction signal. The weights inthe averaging are fixed and are 0.5 respectively for the firstprediction signal and the second prediction signal.

In another example (e.g., VVC), the bi-prediction mode is extendedbeyond simple averaging to allow weighted averaging of the twoprediction signals. For example, P₀[i,j] denotes the first predictionsignal for the pixel at the position (i,j) in the current CU and P₁[i,j]denotes the second prediction signal for the pixel at the position (i,j)in the current CU. The first prediction signal is obtained by interprediction based on the first reference picture and the first motionvector, and the second prediction signal is obtained by inter predictionbased on the second reference picture and the second motion vector. Thebi-prediction signal denoted by P_(bi-pred)[i,j] for the pixel at theposition (i,j) can be calculated according to Eq. (1):

P _(bi-pred)[i,j]=((8−w)×P ₀[i,j]+w×P ₁[i,j]+4)>>3   Eq. (1)

where w denotes the weight for the second prediction signal. In someexamples, the weights are signaled from the encoder side to the decoderside using weight index. For example, five weights are allowed in theweighted averaging bi-prediction, w∈{−2, 3, 4, 5,10}. A BCW weight indexis coded in the bitstream at CU level and the BCW weight index canindicate one of the five weights to use in bi-prediction.

In some related examples, a technique that is referred to as localillumination compensation (LIC) is used. In an example, LIC is used inan inter prediction technique for uni-prediction of inter coded CUs. LICis not applied to bi-prediction. LIC can model local illuminationvariation between current block and its reference block as a function ofvariation between current block template and reference block template.

FIGS. 9A-9C show diagrams illustrating a uni-prediction of an intercoded CU in some examples. In FIG. 9A, a current block (910) is locatedin a current picture for coding. To inter predict the current block(910), a reference block (920) in a reference picture is determined as atemporal prediction of the current block (910). The location of thereference block (920) in the reference picture can have a spatial shiftfrom the location of the current block (910) in the current picture,such as illustrated by a motion vector (930) in FIG. 9A.

In FIG. 9B, current template and reference template respectivelyassociated with the current block (910) and the reference block (920)are shown. In some examples, the current template of the current block(910) includes an above current template (911) and a left currenttemplate (912) as shown in FIG. 9B. The above current template (911)includes adjacent pixels above the current block (910) in the currentpicture. The left current template (912) includes adjacent pixels to theleft of the current block (910) in the current picture.

Similarly, the reference template of the reference block (920) includesan above reference template (921) and a left reference template (922) asshown in FIG. 9B. The above reference template (921) includes adjacentpixels above the reference block (920) in the reference picture. Theleft reference template (922) includes adjacent pixels to the left ofthe reference block (920) in the reference picture.

In some examples, an above template of a block includes one row ofpixels immediately above the block, and a left template of a blockincludes one column of pixels immediately to the left of the block. Asshown in FIG. 9B, the above current template (911) includes a row ofpixels immediately above the current block (910) in the current picture;and the left current template (912) includes a column of pixelsimmediately to the left of the current block (910) in the currentpicture. The above reference template (921) includes a row of pixelsimmediately above the reference block (920) in the reference picture.The left reference template (922) includes a column of pixelsimmediately to the left of the reference block (920) in the referencepicture.

In FIG. 9C, the reference block template (including the above referencetemplate (921) and the left reference template (922)) can be consideredas a temporal prediction of the current block template (including theabove current template (911) and the left current template (912))indicated by the motion vector (930) between the current block (910) andthe reference block (920).

In some examples, according to the local illumination compensation(LIC), samples in a current block can be predicted by applying an LICmodel on samples in the reference block. For example, the current blockhas width w and height h, the reference block also has width w andheight h. For ease of description, the top left corner of the currentblock is assumed to have coordinates (0,0), the top left corner of thereference block is assume to have to have coordinates (0,0). Further,y[i,j] denotes sample value at location (i,j) in the current block for0≤i<w and 0≤j<h, ŷ[i,j] denotes a prediction of the sample value atlocation (i,j) in the current block for 0≤i<w and 0≤j<h, and x[i,j]denotes reconstructed sample value at location (i,j) in the referenceblock for 0≤i<w and 0≤j<h. In some examples, the LIC model can berepresented using Eq. (2):

{circumflex over (y)}[i,j]=α·x[i,j]+β  Eq. (2)

where α denotes a scale parameter and β denotes an offset parameter thatare used to compensate for illumination changes between the currentblock in the current picture and the reference block in the referencepicture.

In some examples, the scale parameter α and the offset parameter β canbe derived based on the current block template (e.g., (911) and (912))and the reference block template (e.g., (921) and (922)). In an example,an LIC flag is signaled to indicate a use of LIC, and no signalingoverhead is required for signaling the scale parameter α and the offsetparameter β.

It is noted that LIC is an inter prediction technique for uni-predictionof inter coded CUs and is not applied to bi-prediction.

According to an aspect of the disclosure, the BCW in the relatedexamples (e.g., VVC) has limited weight precision. In some examples,only a maximum of five values of weight are allowed in the weightedaveraging bi-prediction. In addition, signaling the weight index in thebitstream can add signaling overhead in bitrate.

According to another aspect of the disclosure, LIC can model localillumination variation between a current block and a reference block ofthe current block as a function of illumination variation between acurrent block template of the current block and a reference blocktemplate of the reference block. LIC does not add overhead in bitrate tosignal the scale parameter and the offset parameter. However, LIC is notapplied to bi-prediction.

Some aspects of the disclosure provide techniques to use inbi-prediction with CU-level weights that are of higher weight precision(e.g., than in VVC) without signaling weights in the bitstream.

In some embodiments, in a bi-prediction mode, P₀[i,j] denotes a firstprediction signal for a pixel at a position (i,j) in a current CU andP₁[i,j] denotes a second prediction signal for the pixel at the position(i,j) in the current CU. The bi-prediction signal denoted byP_(bi-pred)[i,j] for the pixel at the position (i,j) can be calculatedas weighted average of the first prediction signal and the secondprediction signal, such as according to Eq. (3):

P _(bi-pred)[i,j]=((2^(n) −w)×P ₀[i,j]+w×P ₁[i,j]+2^(n−1))>>n=P₀[i,j]+(w·(P ₁[i,j]=P ₀[i,j])+2^(n−1))>>n   Eq. (3)

where w denotes a weight and n denotes a pre-determined shift parameter.In some examples, the weight w is an integer and 0<w<2 ^(n). In anembodiment, n is set to 5 when the first prediction signal P₀ and thesecond prediction signal P₁ are represented using 10 bits, thus thecomputation in Eq. (3) can be done with 16 bits signed arithmetic.

According to some embodiments, the weight w can be determined based on acurrent template of the current CU and reference templates of thereference CUs, and thus CU level weight signaling is not needed in someexamples.

FIG. 10 shows a diagram of using bi-prediction for coding a videosequence (1000) according to some embodiments of the disclosure.

In the FIG. 10 example, the video sequence (1000) includes a pluralityof picture frames, such as frames (1001)-(1003) and the like. The frame(1001) is a current frame for coding, and the frames (1002) and (1003)are coded (encoded or decoded) before the frame (1001). In someexamples, one of the frames (1002) and (1003) is before the frame (1001)in a display order of the video sequence (1000), and the other of theframes (1002) and (1003) is after the frame (1001) in the display order.It is noted that additional frames may or may not exist between theframe (1002) and the frame (1001) or between the frame (1001) and theframe (1003). In some other examples, both of the frames (1002) and(1003) are before the frame (1001) in the display order or both of theframes (1002) and (1003) are after the frame (1001) in the displayorder.

In the FIG. 10 example, a current block (1010) is located in the currentpicture, such as the frame (1001), for coding. To inter predict thecurrent block (1010) in a bi-prediction mode, a first reference block(1020) in a first reference picture, such as the frame (1002) and asecond reference block (1030) in a second reference picture, such as theframe (1003) are determined. The location of the first reference block(1020) in the frame (1002) can have a first spatial shift from thelocation of the current block (1010) in the frame (1001), such asillustrated by a motion vector (1025) denoted by mv₀ in FIG. 10. Thelocation of the second reference block (1030) in the frame (1003) canhave a second spatial shift from the location of the current block(1010) in the frame (1001), such as illustrated by a motion vector(1035) denoted by mv₁ in FIG. 10. The first reference block (1020) canbe referred to as a first prediction of the current block (1010), andcan be denoted by P₀. The second reference block (1030) can be referredto as a second prediction of the current block (1010), and can bedenoted by P₁. The current block (1010) can be predicted by weightedaverage of the first prediction P₀ and the second prediction P₁.

In some embodiments, the current template of the current block (1020),the reference template of the first reference block (1020) and thereference template of the second reference block (1030) are used todetermine the weight w in the bi-prediction mode.

In some examples, the current template of the current block (1010) isreferred to as a current template T_(c). The current template T_(c)includes decoded pixels that are adjacent to the current block (1010).In some examples, the current template T_(c) includes a row of pixels(e.g., shown by (1011)) that is immediately above the current block(1010) and includes a column of pixels (e.g., shown by (1012)) that isimmediately left to the current block (1010).

The reference template of the first reference block (1020) is referredto as a first reference template T₀. The first reference template T₀includes decoded pixels that are adjacent to the first reference block(1020). In some examples, the first reference template T₀ includes a rowof pixels (e.g., shown by (1021)) that is immediately above the firstreference block (1020) and includes a column of pixels (e.g., shown by(1022)) that is immediately left to the first reference block (1020).

The reference template of the second reference block (1030) is referredto as a second reference template T₁. The second reference template T₁includes decoded pixels that are adjacent to the second reference block(1030). In some examples, the second reference template T₁ includes arow of pixels (e.g., shown by (1031)) that is immediately above thesecond reference block (1030) and includes a column of pixels (e.g.,shown by (1032)) that is immediately left to the second reference block(1030).

It is noted that, in some examples, the current template T_(c) can haveany suitable shape, and the first reference template T₀ and the secondreference template T₁ corresponding to the current template T_(c) can bedetermined based on the motion vectors mv₀ and mv₁.

According to an aspect of the disclosure, when coding (encoding ordecoding) the current block (1010), the current template T_(c) has beenreconstructed. The first reference picture (1002) and the secondreference picture (1003) have been reconstructed, thus the firstreference template T₀ and the second reference template T₁ arereconstructed. The weight w is then determined based on the currenttemplate T_(c), the first reference template T₀ and the second referencetemplate T₁. The weight w can be computed at the encoder and thedecoder, and thus in some examples, the weight w is not signaled in thebitstream.

It is noted that the weight w can be computed using any suitabletechniques.

In some embodiments, a cost function can be formed with a cost dependingon the weight w. Then, the weight w can be determined as an argumentthat minimizes the cost of the cost function.

In some examples, the first reference template T₀ and the secondreference template T₁ are applied according to Eq. (3) to determine apredicted current template T_(w) as a function of the weight w. Forexample, the predicted current template T_(w) at a position (i,j) in thecurrent template T_(c) can be calculated according to Eq. (4):

T _(w)[i,j]=T ₀[i,j]+(w×(T ₁[i,j]−T ₀[i,j])+2^(n−1))>>n   Eq. (4)

In an embodiment, a difference of T_(w)[i,j] and T_(c)[i,j] can be usedto calculate a cost function.

In some examples, a cost function can be formed according to Eq. (5):

cost function=∥T _(c) −T _(w∥) ²=Σ_(locations in the current template)(T_(c)[i,j]−T _(w)[i,j])²   Eq. (5)

The weight w is the argument which minimizes the cost of the costfunction. In an example, the weight w is subject to the constraint that0<w<2^(n), n is a positive integer. In an embodiment, n is set to 5 whenthe first prediction signal P₀ and the second prediction signal P₁ arerepresented using 10 bits, thus the computation in Eq. (4) and Eq. (5)can be done with 16 bits signed arithmetic.

In some examples, the weight w is determined approximately by ordinaryleast squares with fixed-point arithmetic and then clipped to the range[a,b], where a and b are predetermined integers.

After the weight w is determined, the current block (1010) can bepredicted in the bi-prediction mode as weighted average of the firstprediction P₀ and second prediction P₁, such as using Eq. (3).

FIG. 11 shows a flow chart outlining a process (1100) that is executedin a bi-prediction mode according to an embodiment of the disclosure.The process starts at (S1101) and proceeds to (S1110).

At (S1110), a current block (e.g., the current block (1010)) isdetermined for coding in the bi-prediction mode, then a first motionvector mv₀, a first reference picture, a second motion vector mv₁ and asecond reference picture are determined. Based on the first motionvector mv₀ and the first reference picture, the first prediction P₀(e.g., the first reference block (1020)) is determined; and based on thesecond motion vector mv₁ and the second reference picture, the secondprediction P₁ (e.g., the second reference block (1030)) is determined.Further, the current template T_(c) (e.g., (1011) and (1012)) isdetermined.

At (S1120), the first reference template T₀ and the second referencetemplate T₁ are determined. In some examples, the first referencetemplate T₀ is determined based on the current template T_(c) and thefirst motion vector mv₀; and the second reference template T₁ isdetermined based on the current template T_(c) and the second motionvector mv₁.

At (S1130), weight(s) to minimize the cost of the cost function is (are)determined. For example, the cost function can be formed based on Eq.(4) and Eq. (5) as a function of the weight w. Then, the weight w isdetermined to minimize the cost of the cost function.

At (S1140), then bi-prediction can be calculated as weighted average ofthe first prediction P₀ and the second prediction P₁ based on thedetermined weight(s).

According to an aspect of the disclosure, a plurality of weightparameters can be used in the bi-prediction mode.

In some examples, three weight parameters are used in the bi-predictionmode. For example, in the bi-prediction mode, the bi-prediction signaldenoted by P_(bi-pred)[i,j] for the pixel at the position (i,j) in thecurrent CU (e.g., current block (1010)) can be calculated as weightedaverage of the first prediction signal P₀[i,j] and the second predictionsignal P₁[i,j] according to a prediction model, such as a predictionmodel according to Eq. (6):

P _(bi-pred)[i,j]=(w ₀ ×P ₀[i,j])+w ₁ ×P ₁[i,j]+w ₂)>>n   Eq. (6)

where w₀, w₁, w₂ are weight parameters (also referred to as weights) ofthe prediction model and n is a pre-determined shift parameter. Theweight parameters w₀, w₁, w₂ can be derived from the templates (e.g.,the current template, the first reference template and the secondreference template) by fixed-point arithmetic.

The values of the weight parameters w₀, w₁, w₂ can be determined basedon the pixels in the current template T_(c) and in the first and secondreference templates T₀ and T₁. In an example, a predicted currenttemplate T_(w) can be formed as a function of the weight parameters. Forexample, the predicted current template T_(w) at a position (i,j) in thecurrent template T_(c) can be represented according to Eq. (7):

T _(w)[i,j]=(w ₀ ×T ₀[i,j]+w ₁ ×T ₁[i,j]+w ₂)>>n   Eq. (7)

In some examples, a cost function can be formed according to Eq. (5)using the predicted template T_(w) and the current template T_(c), andthus the cost function is a function of the weight parameters. In anexample, the weight parameters w₀, w₁, w₂ can be determined as theargument which minimizes the cost of the cost function with theconstraint that 0≤T_(w)[i,j]<2^(b) (for all positions in the currenttemplate T_(c)) where b is the bit-depth of the pixels.

In an example, the weight parameters w₀, w₁, w₂ are determinedapproximately by ordinary least squares with fixed-point arithmeticusing Cramer's rule. In some examples, the values of the weightparameters can be clipped. In an example, w_(i) is clipped to the range[a_(i),b_(i)] where a_(i) and b_(i) are predetermined integers, i∈{0, 1,2}.

In some examples, two weight parameters are used in the bi-predictionmode. For example, in the bi-prediction mode, the bi-prediction signaldenoted by P_(bi-pred)[i,j] for the pixel at the position (i,j) in thecurrent CU (e.g., current block (1010)) can be calculated as weightedaverage of the first prediction signal P₀[i,j] and the second predictionsignal P₁[i,j] according to a prediction model, such as a predictionmodel according Eq. (8):

P _(bi-pred)[i,j]=(w ₀ ×P ₀[i,j])+w ₁ ×P ₁[i,j]+C)>>n   Eq. (8)

where w₀, w₁ are weight parameters (also referred to as weights) of theprediction model that can be derived from the templates (e.g., thecurrent template, the first reference template and the second referencetemplate) by fixed-point arithmetic. The parameter C is a predeterminedvalue for rounding and n is a pre-determined shift parameter.

The values of the weight parameters w₀, w₁ can be determined based onthe pixels in the current template T_(c) and in the first and secondreference templates T₀ and T₁. In an example, a predicted currenttemplate T_(w) can be formed as a function of the weight parameters. Forexample, the predicted current template T_(w) at a position (i,j) in theregion of the current template T_(c) can be represented according to Eq.(9):

T _(w)[i,j]=(w ₀ ×T ₀[i,j]+w ₁ ×T ₁[i,j]+C)>>n   Eq. (9)

In some examples, a cost function can be formed according to Eq. (5)using the predicted template T_(w) and the current template T_(c), andthus the cost function is a function of the weight parameters. In anexample, the weight parameters w₀, w₁ can be determined as the argumentwhich minimizes the cost of the cost function with the constraint that0≤T_(w)[i,j]<2^(b) (for all positions in the current template T_(c))where b is the bit-depth of the pixels.

In an example, the weight parameters w₀, w₁ are determined approximatelyby ordinary least squares with fixed-point arithmetic using Cramer'srule. In some examples, the values of the weight parameters can beclipped. In an example, w_(i) is clipped to the range [a_(i),b_(i)]where a_(i) and b_(i) are predetermined integers, i∈{0,1}.

According to an aspect of the disclosure, at the encoder side, weightparameter(s) for use in the bi-prediction mode can be determined jointlywith the determination of the motion vectors mv₀ and mv₁.

FIG. 12 shows a flow chart outlining a process (1200) according to someembodiments of the disclosure. In some examples, the process (1200) isused at an encoder side to jointly determine the weight parameter(s) andthe first motion vector mv₀ and the second motion vector mv₁ for use inthe bi-prediction mode. The process (1200) performs motion vectorrefinements with an initial first motion vector mv₀′ and an initialsecond motion vector mv₁′ based on a pre-defined search pattern. Theprocess (1200) can use a pre-defined bi-prediction model, and apre-defined cost function based on fixed-point arithmetic to determinethe best motion vectors mv₀ and mv₁ and the best weight(s). The bestmotion vectors mv₀ and mv₁ can be suitably informed to a decoder side,and the best weight(s) are not signaled to the decoder side. The decoderside can determined the weights based on the informed motion vectors(e.g., the best motion vectors mv₀ and mv₁). The process starts at(S1201) and proceeds to (S1210)

At (S1210), the initial first motion vector mv₀′, the initial secondmotion vector mv₁′ and the current template T_(c) are determined, and afirst refinement to mv₀′ denoted by dmv₀ is initially set to 0, and asecond refinement to mv₁′ denoted by dmv₁ is initially set to 0. Theinitial first motion vector mv₀′ and the initial second motion vectormv₁′ can be determined by any suitable technique.

At (S1220), the refined first motion vector

is determined based on the initial first motion vector mv₀′ and thefirst refinement dmv₀, and the refined second motion vector

is determined based on the initial second motion vector mv₁′ and thesecond refinement dmv₁.

At (S1230), the first reference template T₀ is determined based on thecurrent template T_(c) and the refined first motion vector

, and the second reference template T₁ is determined based on thecurrent template T_(c) and the refined second motion vector

.

At (S1240), a predefined bi-prediction model with weight parameter(s)(e.g., Eq. (3), Eq. (6), Eq. (8)) can be used to represent the predictedtemplate T_(w) based on the first reference template T₀ and the secondreference template T₁, such as shown in Eq. (4), Eq. (7) and Eq. (9).Thus, the predicted template T_(w) is represented as a function of theweight parameter(s). Then, a pre-defined cost function can be used torepresent a cost based on the predicted template T_(w) and the currenttemplate T_(c), such as according to Eq. (5). Thus, the cost is afunction of the weight parameter(s). Further, the weight parameters(s)are calculated to minimize the cost of the cost function. The minimumcost associated with the present refinements dmv₀ and dmv₁ is referredto as newly calculated cost. The calculated weight parameter(s) isassociated with the newly calculated cost. In some examples, thecomputation can be performed by ordinary least squares with fixed-pointarithmetic using Cramer's rule.

At (S1250), the newly calculated cost is compared with previous bestcost to update t best cost. In an example, when the newly calculatedcost is smaller than the previous best cost, the newly calculated costis stored as the best cost, the calculated weight parameter(s)associated with the newly calculated cost is kept as the best weigh(s)in association with the best cost, and the current refined motionvectors

and

(with the present refinements dmv₀ and dmv₁ applied on the initialmotion vectors mv₀′ and mv₁′) associated with the newly calculated costare kept as the best refined motion vectors in association with the bestcost. In another example, when the newly calculated cost is equal orhigher than the previous best cost, the previous best cost is stillstored as the best cost and the previous best weight(s) associated withthe previous best cost is still kept as the best weight(s) inassociation with the best cost and previous best refined motion vectorsassociated with the previous best cost are still kept as the bestrefined motion vectors in association with the best cost.

At (S1260), when the pre-defined search pattern is completely searchedover, the process proceeds to (S1280); otherwise, the process proceedsto (S1270).

At (S1270), the first refinement dmv₀ and the second refinement dmv₁ areupdated according to the pre-defined search pattern, and the processreturns to (S1220).

At (S1280), the first prediction P₀ and the second prediction P₁ aredetermined (e.g., calculated) based on the best refined motion vectorsin association with the best cost.

At (S1290), the bi-prediction can be computed based on the firstprediction P₀, the second prediction P₁ and the best weight(s) inassociation with the best cost.

FIG. 13 shows a flow chart outlining a process (1300) according to anembodiment of the disclosure. The process (1300) can be used in a videoencoder. In various embodiments, the process (1300) is executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video encoder (403), the processing circuitrythat performs functions of the video encoder (603), the processingcircuitry that performs functions of the video encoder (703), and thelike. In some embodiments, the process (1300) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1300). Theprocess starts at (S1301) and proceeds to (S1310).

At (S1310), a bi-prediction mode without weight signaling is determinedfor coding a coding block in a current picture. In an example, theencoder may perform an evaluation and based on the evaluation, determineto use the bi-prediction mode without weight signaling for coding thecoding block.

At (S1320), motion vectors, such as a first motion vector associatedwith a first reference picture and a second motion vector associatedwith a second reference picture, and weight(s) for a bi-prediction ofthe coding block are determined.

In some embodiments, the first motion vector and the second motionvector are determined, and then weight(s) are determined. In someexamples, after the motion vectors are determined, reference templatesin the reference pictures are determined based on a current template ofthe coding block and the motion vectors. For example, a first referencetemplate in the first reference picture is determined based on thecurrent template of the coding block and the first motion vector; and asecond reference template in the second reference picture is determinedbased on the current template of the coding block and the second motionvector.

According to an aspect of the disclosure, the current template of thecurrent block includes one or more reconstructed samples that areneighboring to the coding block. In some examples, the current templateincludes one or more rows of samples above the coding block and/or oneor more columns of samples to the left of the coding block. In anexample, the current template includes a row of samples that isimmediately above the coding block and/or a column of samples that isimmediately to the left of the coding block.

In some embodiments, weight(s) for use in the bi-prediction mode isdetermined based on the first reference template, the second referencetemplate and the current template.

In some embodiments, the weight(s) is determined to minimize a cost of apredefined cost function. The predefined cost function is based on thefirst reference template, the second reference template and the currenttemplate. For example, the predefined cost function is based onrespective samples differences of the current template to a predictedcurrent template, such as Eq. (5).

The predicted current template is predicted based on the first referencetemplate and the second reference template using a predefinedbi-prediction model with one or more weight parameters.

In some examples, the predefined bi-prediction model includes threeweight parameters, the predicted current template can be represented,for example, according to Eq. (7). In an example, values of the threeweight parameters in the predefined bi-prediction model are determinedby ordinary least squares, such as with fixed-point arithmetic usingCramer's rule.

In some examples, the predefined bi-prediction model includes two weightparameters, the predicted current template can be represented, forexample, according to Eq. (9). In an example, values of the two weightparameters in the predefined bi-prediction model are determined byordinary least squares, such as with fixed-point arithmetic usingCramer's rule.

In some examples, the predefined bi-prediction model includes one weightparameter, the predicted current template can be represented, forexample, according to Eq. (4). In an example, a value of the weightparameter in the predefined bi-prediction model is determined byordinary least squares, such as with fixed-point arithmetic.

In some examples, the value(s) of the weight parameters are clipped inpredetermined ranges respectively for the weight parameters.

In some embodiments, the first motion vector, the second motion vector,and weight(s) are determined jointly. An example to determine the firstmotion vector, the second motion vector, and weight(s) jointly has beendescripted with reference to FIG. 12.

At (S1330), the coding block is reconstructed using the bi-predictionwith the weight(s). In some examples, the predefined bi-prediction modelincludes three weight parameters, the coding block can be reconstructed,for example, according to Eq (6). In some examples, the predefinedbi-prediction model includes two weight parameters, the coding block canbe reconstructed, for example, according to Eq (8). In some examples,the predefined bi-prediction model includes one weight parameter, thecoding block can be reconstructed, for example, according to Eq (3).

At (S1340), information of the coding block is encoded in the bitstreamwithout weight signaling. The information indicates the bi-predictionmode without weight signaling in the bitstream. Then, the processproceeds to (S1399) and terminates.

The process (1300) can be suitably adapted. Step(s) in the process(1300) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

FIG. 14 shows a flow chart outlining a process (1400) according to anembodiment of the disclosure. The process (1400) can be used in a videodecoder. In various embodiments, the process (1400) is executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the video decoder (510), and the like. Insome embodiments, the process (1400) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1400). Theprocess starts at (S1401) and proceeds to (S1410).

At (S1410), information of a coding block in a current picture isdecoded from a bitstream. The information indicates a bi-prediction modewithout weight signaling.

At (S1420), motion vectors for a bi-prediction of the coding block aredetermined. For example, a first motion vector associated with a firstreference picture and a second motion vector associated with a secondreference picture are determined. The motion vectors can be determinedby any suitable techniques. In some examples, the motion vectors can bedetermined based on indexes to candidate lists, the indexes can bedecoded from the bitstream.

At (S1430), reference templates in the reference pictures are determinedbased on a current template of the coding block and the motion vectors.For example, a first reference template in the first reference pictureis determined based on the current template of the coding block and thefirst motion vector; and a second reference template in the secondreference picture is determined based on the current template of thecoding block and the second motion vector.

According to an aspect of the disclosure, the current template of thecurrent block includes one or more reconstructed samples that areneighboring to the coding block. In some examples, the current templateincludes one or more rows of samples above the coding block and/or oneor more columns of samples to the left of the coding block. In anexample, the current template includes a row of samples that isimmediately above the coding block and/or a column of samples that isimmediately to the left of the coding block.

At (S1440), a weight for use in the bi-prediction mode is determinedbased on the first reference template, the second reference template andthe current template.

In some embodiments, the weight is determined to minimize a cost of apredefined cost function. The predefined cost function is based on thefirst reference template, the second reference template and the currenttemplate. For example, the predefined cost function is based onrespective samples differences of the current template to a predictedcurrent template, such as using Eq. (5).

The predicted current template is predicted based on the first referencetemplate and the second reference template using a predefinedbi-prediction model with one or more weight parameters.

In some examples, the predefined bi-prediction model includes threeweight parameters, the predicted current template can be represented,for example, according to Eq. (7). In an example, values of the threeweight parameters in the predefined bi-prediction model are determinedby ordinary least squares, such as with fixed-point arithmetic usingCramer's rule.

In some examples, the predefined bi-prediction model includes two weightparameters, the predicted current template can be represented, forexample, according to Eq. (9). In an example, values of the two weightparameters in the predefined bi-prediction model are determined byordinary least squares, such as with fixed-point arithmetic usingCramer's rule.

In some examples, the predefined bi-prediction model includes one weightparameter, the predicted current template can be represented, forexample, according to Eq. (4). In an example, a value of the weightparameter in the predefined bi-prediction model is determined byordinary least squares, such as with fixed-point arithmetic.

In some examples, the value(s) of the weight parameters are clipped inpredetermined ranges respectively for the weight parameters.

At (S1450), the coding block is reconstructed using the bi-predictionwith the weight(s). In some examples, the predefined bi-prediction modelincludes three weight parameters, the coding block can be reconstructed,for example, according to Eq (6). In some examples, the predefinedbi-prediction model includes two weight parameters, the coding block canbe reconstructed, for example, according to Eq (8). In some examples,the predefined bi-prediction model includes one weight parameter, thecoding block can be reconstructed, for example, according to Eq (3).

Then, the process proceeds to (S1499) and terminates.

It is noted that in some examples, when any of the neighborhoods of thecoding block is not available, predetermined weights (e.g., defaultsweights and the like) may be used.

The process (1400) can be suitably adapted. Step(s) in the process(1400) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 15 shows a computersystem (1500) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system (1500) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1500).

Computer system (1500) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1501), mouse (1502), trackpad (1503), touchscreen (1510), data-glove (not shown), joystick (1505), microphone(1506), scanner (1507), camera (1508).

Computer system (1500) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1510), data-glove (not shown), or joystick (1505), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1509), headphones(not depicted)), visual output devices (such as screens (1510) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1500) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1520) with CD/DVD or the like media (1521), thumb-drive (1522),removable hard drive or solid state drive (1523), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1500) can also include an interface (1554) to one ormore communication networks (1555). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1549) (such as,for example USB ports of the computer system (1500)); others arecommonly integrated into the core of the computer system (1500) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1500) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1540) of thecomputer system (1500).

The core (1540) can include one or more Central Processing Units (CPU)(1541), Graphics Processing Units (GPU) (1542), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1543), hardware accelerators for certain tasks (1544), graphicsadapters (1550), and so forth. These devices, along with Read-onlymemory (ROM) (1545), Random-access memory (1546), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(1547), may be connected through a system bus (1548). In some computersystems, the system bus (1548) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (1548), or through a peripheral bus (1549). In anexample, the screen (1510) can be connected to the graphics adapter(1550). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (1541), GPUs (1542), FPGAs (1543), and accelerators (1544) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1545) or RAM (1546). Transitional data can be also be stored in RAM(1546), whereas permanent data can be stored for example, in theinternal mass storage (1547). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1541), GPU (1542), massstorage (1547), ROM (1545), RAM (1546), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1500), and specifically the core (1540) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1540) that are of non-transitorynature, such as core-internal mass storage (1547) or ROM (1545). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1540). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1540) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1546) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1544)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video processing in a decoder,comprising: decoding information of a coding block in a current picturefrom a bitstream, the information indicating a bi-prediction mode,wherein weights associated with the bi-prediction mode are not signaledin the bitstream; determining a first motion vector associated with afirst reference picture and a second motion vector associated with asecond reference picture for a bi-prediction of the coding block;determining a first reference template in the first reference picturebased on a current template of the coding block and the first motionvector; determining a second reference template in the second referencepicture based on the current template of the coding block and the secondmotion vector; calculating a weight for use in the bi-prediction modebased on the first reference template, the second reference template andthe current template; and reconstructing the coding block using thebi-prediction with the calculated weight.
 2. The method of claim 1,wherein the current template comprises one or more reconstructed samplesthat are neighboring to the coding block.
 3. The method of claim 2,wherein the current template comprises at least one of: one or more rowsof samples above the coding block; or one or more columns of samples toa left of the coding block.
 4. The method of claim 2, wherein thecurrent template comprises at least one of: a row of samples that isimmediately above the coding block; or a column of samples that isimmediately to a left of the coding block.
 5. The method of claim 1,wherein the determining the weight for use in the bi-prediction modefurther comprises: determining the weight that minimizes a predefinedcost function that is based on the first reference template, the secondreference template and the current template.
 6. The method of claim 5,wherein the predefined cost function is based on respective samplesdifferences of the current template to a predicted current template thatis predicted based on the first reference template and the secondreference template using a predefined bi-prediction model with one ormore weight parameters.
 7. The method of claim 1, wherein thedetermining the weight for use in the bi-prediction mode furthercomprises: determining values of three weight parameters in a predefinedbi-prediction model by ordinary least squares.
 8. The method of claim 1,wherein the determining the weight for use in the bi-prediction modefurther comprises: determining values of two weight parameters in apredefined bi-prediction model by ordinary least squares.
 9. The methodof claim 1, wherein the determining the weight for use in thebi-prediction mode further comprises: determining a value of one weightparameter in a predefined bi-prediction model by ordinary least squares.10. The method of claim 1, wherein the determining the weight for use inthe bi-prediction mode further comprises: clipping the weight in apredetermined range.
 11. An apparatus for video decoding, comprisingprocessing circuitry configured to: decode information of a coding blockin a current picture from a bitstream, the information indicating abi-prediction mode wherein weights associated with the bi-predictionmode are not signaled in the bitstream; determine a first motion vectorassociated with a first reference picture and a second motion vectorassociated with a second reference picture for a bi-prediction of thecoding block; determine a first reference template in the firstreference picture based on a current template of the coding block andthe first motion vector; determine a second reference template in thesecond reference picture based on the current template of the codingblock and the second motion vector; calculate a weight for use in thebi-prediction mode based on the first reference template, the secondreference template and the current template; and reconstruct the codingblock using the bi-prediction with the calculated weight.
 12. Theapparatus of claim 11, wherein the current template comprises one ormore reconstructed samples that are neighboring to the coding block. 13.The apparatus of claim 12, wherein the current template comprises atleast one of: one or more rows of samples above the coding block; or oneor more columns of samples to a left of the coding block.
 14. Theapparatus of claim 12, wherein the current template comprises at leastone of: a row of samples that is immediately above the coding block; ora column of samples that is immediately to a left of the coding block.15. The apparatus of claim 11, wherein the processing circuitry isconfigured to: determine the weight that minimizes a predefined costfunction that is based on the first reference template, the secondreference template and the current template.
 16. The apparatus of claim15, wherein the predefined cost function is based on respective samplesdifferences of the current template to a predicted current template thatis predicted based on the first reference template and the secondreference template using a predefined bi-prediction model with one ormore weight parameters.
 17. The apparatus of claim 11, wherein theprocessing circuitry is configured to: determine values of three weightparameters in a predefined bi-prediction model by ordinary leastsquares.
 18. The apparatus of claim 11, wherein the processing circuitryis configured to: determine values of two weight parameters in apredefined bi-prediction model by ordinary least squares.
 19. Theapparatus of claim 11, wherein the processing circuitry is configuredto: determine a value of one weight parameter in a predefinedbi-prediction model by ordinary least squares.
 20. The apparatus ofclaim 11, wherein the processing circuitry is configured to: clip theweight in a predetermined range.